Merge pull request #42 from dotkernel/di-docs

added di docs

Author: arhimede

docs/book/v5/core-features/dependency-injection.md

@@ -0,0 +1,61 @@
+# Dependency Injection
+
+Dependency injection is a design pattern used in software development to implement inversion of control. In simpler
+terms, it's the act of providing dependencies for an object during instantiation.
+
+In PHP, dependency injection can be implemented in various ways, including through constructor injection, setter
+injection and property injection.
+
+DotKernel API, through its [dot-dependency-injection](https://github.com/dotkernel/dot-dependency-injection) package
+focuses only on constructor injection.
+
+## Usage
+
+**DotKernel API** comes out of the box with the
+[dot-dependency-injection](https://github.com/dotkernel/dot-dependency-injection) package, which provides all we need for
+injecting dependencies into any object you want.
+
+`dot-dependency-injection` determines the dependencies by looking at the `#[Inject]` attribute, added to the constructor
+of a class. Dependencies are specified as separate parameters of the `#[Inject]` attribute.
+
+For our example we will inject `UserService` and `config` dependencies into a `UseHandler`.
+
+```php
+use Dot\DependencyInjection\Attribute\Inject;
+
+class UserHandler implements RequestHandlerInterface
+{
+    #[Inject(
+        UserService::class,
+        "config",
+    )]
+    public function __construct(
+        protected UserServiceInterface $userService,
+        protected array $config,
+    ) {
+    }
+}
+```
+
+> If your class needs the value of a specific configuration key, you can specify the path using dot notation:
+> `config.example`
+
+The next step is to register the class in the `ConfigProvider` under `factories` using
+`Dot\DependencyInjection\Factory\AttributedServiceFactory::class`
+
+```php
+public function getDependencies(): array
+{
+    return [
+        'factories' => [
+            UserHandler::class => AttributedServiceFactory::class
+        ]
+    ];
+}
+```
+
+That's it. When your object is instantiated from the container, it will automatically have its
+dependencies resolved.
+
+> Dependencies injection is available to any object within DotKernel API. For example, you can inject dependencies in a
+> service, a handler and so on, simply by registering it in the `ConfigProvider`.

mkdocs.yml

@@ -31,6 +31,7 @@ nav:
           - "Content Validation": v5/core-features/content-validation.md
           - "Exceptions": v5/core-features/exceptions.md
           - "CORS": v5/core-features/cors.md
+          - "Dependency Injection": v5/core-features/dependency-injection.md
       - Commands:
           - "Create admin account": v5/commands/create-admin-account.md
           - "Generate database migrations": v5/commands/generate-database-migrations.md